In some document imaging systems, the imaging sensor or capture unit must locate the document on the scanning surface in order to focus properly. If the document cannot be located properly, image quality will degrade. For example, a document that is not flat against the scanning surface because of wrinkles or folds in the document results in blurry text and out-of-focus graphics. Some of these imaging systems use a white background that is placed behind the document to locate the document's vertical position relative to the scanning surface. Even so, conventional imaging systems typically produce images with reduced quality when the document does not rest flat against the scanning surface.